Diffuser for a centrifugal compressor

Abstract

A diffuser for a centrifugal compressor in which the diffuser has a plurality of passageways that each include a diffuser inlet region, a diffuser throat region, and a diffusion region. Within the diffuser inlet region are positioned pairs of opposed ridges that disrupt the boundary layer growth and minimize aerodynamic blockage at the throat region. The diffusion region includes a first diffusion region downstream of the throat region and that has a first area expansion ratio, and the second diffusion region that includes flow dividers to allow a total area expansion rate within the second diffusion region that is about twice that of the area expansion rate in the first diffusion region.

What is claimed is:  
     
       1. A diffuser for a centrifugal compressor that includes an impeller rotatably carried within a casing, said diffuser comprising: 
       a plurality of substantially linearly-extending diffuser passageways having respective longitudinal axes disposed tangentially to an imaginary circle having its center coincident with the impeller axis, the diffuser passageways including a diffuser inlet region commencing adjacent the impeller periphery, a diffuser throat region downstream of the diffuser inlet region, and a diffuser outlet region downstream of the diffuser throat region, wherein the diffuser passageways are each bounded by a pair of circumferentially spaced diffuser panels having respective leading edges adjacent the impeller periphery and that lie on a diffuser leading edge circle, and trailing edges spaced radially outwardly of and circumferentially offset from the leading edges and that lie on a diffuser trailing edge circle; and  
       a pair of opposed ridges extending substantially longitudinally relative to and within the diffuser inlet region between the impeller periphery and the diffuser leading edge circle, each ridge varying in height along the diffuser inlet region and extending partially inwardly into the diffuser passageway, wherein the ridges are positioned between and are spaced from the leading edges of adjacent diffuser panels for mixing of air leaving the impeller and entering the diffuser passageway, to reduce boundary layer buildup within the diffuser passageway upstream of the diffuser throat region.  
     
     
       2. A diffuser in accordance with  claim 1 , wherein the pair of ridges are substantially parallel with the diffuser passageway longitudinal axis. 
     
     
       3. A diffuser in accordance with  claim 1 , including ledges that extend partially inwardly into the diffuser inlet region, wherein the ledges extend inwardly relative to the compressor impeller from the diffuser leading edges to promote mixing of air entering the diffuser passageways and to reduce boundary layer build-up. 
     
     
       4. A diffuser in accordance with  claim 3 , wherein the ledges extend from the diffuser panel leading edges toward the impeller periphery. 
     
     
       5. A diffuser in accordance with  claim 1 , wherein the diffuser throat region is defined by a constant cross-sectional area section between the diffuser inlet region and the diffuser outlet region. 
     
     
       6. A diffuser in accordance with  claim 1 , wherein the diffuser outlet region is defined by substantially linear wall surfaces of the diffuser panels. 
     
     
       7. A diffuser in accordance with  claim 6 , wherein the diffuser wall surfaces diverge at a first divergence included angle. 
     
     
       8. A diffuser in accordance with  claim 6 , wherein the diffuser outlet region includes a first diffusion region and a second diffusion region. 
     
     
       9. A diffuser in accordance with  claim 8 , wherein the wall surfaces of the diffuser panels within the second diffusion region define a second divergence included angle. 
     
     
       10. A diffuser in accordance with  claim 9 , wherein the second divergence included angle is greater than the first divergence included angle. 
     
     
       11. A diffuser in accordance with  claim 9 , including a flow divider positioned within the second diffusion region. 
     
     
       12. A diffuser in accordance with  claim 11 , wherein the flow divider is positioned between and is spaced from adjacent diffuser panels to define respective sub-diffusion regions. 
     
     
       13. A diffuser in accordance with  claim 12 , wherein the sub-diffusion regions together have an expansion area ratio rate that is larger than the area ratio rate in the first diffusion region. 
     
     
       14. A diffuser for a centrifugal compressor that includes an impeller rotatably carried within a casing, said diffuser comprising: 
       a plurality of substantially linearly-extending diffuser passageways having respective longitudinal axes disposed tangentially to an imaginary circle having its center coincident with the impeller axis, the diffuser passageways including a diffuser inlet region commencing adjacent the impeller periphery, a diffuser throat region downstream of the diffuser inlet region, and a diffuser outlet region downstream of the diffuser throat region, wherein the diffuser outlet region is defined by substantially linear wall surfaces of the diffuser panels and includes a first diffusion region and a second diffusion region, wherein the diffuser passageways are each bounded by a pair of circumferentially spaced diffuser panels having respective leading edges adjacent the impeller periphery and that lie on a diffuser leading edge circle, and having trailing edges spaced radially outwardly of and circumferentially offset from the leading edges and that lie on a diffuser trailing edge circle, wherein the wall surfaces of the diffuser panels within the second diffusion region define a second divergence included angle, including a flow divider positioned within the second diffusion region; and  
       at least one ridge extending substantially longitudinally relative to and within the diffuser inlet region between the impeller periphery and the diffuser leading edge circle, and extending inwardly into the diffuser passageway, wherein the at least one ridge is positioned between and is spaced from the leading edges of adjacent diffuser panels for mixing of air leaving the impeller and entering the diffuser passageway to reduce boundary layer buildup upstream of the diffuser throat region, wherein the diffuser flow divider is carried within an annular outlet passageway extending downstream of the diffuser outlet region.  
     
     
       15. A diffuser in accordance with  claim 14 , wherein the diffuser flow divider is curved to turn diffuser outlet airflow in a direction substantially parallel to the impeller axis of rotation. 
     
     
       16. A diffuser in accordance with  claim 15 , wherein the diffuser flow divider extends substantially across a flow channel defined by an inner annular wall and an outer annular wall that is spaced outwardly from the inner annular wall to define the annular outlet passageway. 
     
     
       17. A diffuser in accordance with  claim 16 , wherein the annular outlet passageway turns air exiting from the diffuser outlet through an angle greater than 90°. 
     
     
       18. A diffuser in accordance with  claim 14 , including deswirler splitter vanes positioned within the annular outlet passageway and between adjacent diffuser flow dividers. 
     
     
       19. A diffuser in accordance with  claim 18 , wherein the deswirler splitter vanes extend from an outlet opening in the annular outlet passageway and terminate at a point spaced downstream of the diffuser panel trailing edges. 
     
     
       20. A method for increasing the efficiency of diffusion for diffusing air that exits from the impeller of a centrifugal compressor, said method comprising: 
       providing a pair of opposed ridges extending substantially longitudinally relative to and within a diffuser inlet region between the impeller periphery and an imaginary circle defined by a plurality of diffuser panel leading edges, each ridge extending partially inwardly into the diffuser inlet region for mixing of air leaving the impeller and entering the diffuser inlet region to reduce boundary layer buildup within the diffuser inlet region;  
       diffusing impeller outlet air flow in a first diffusion region downstream of the diffuser inlet region through a first passageway area ratio;  
       dividing outlet flow from the first diffusion region into two flows in a pair of second diffusion regions downstream of the first diffusion region; and  
       diffusing flow within the first diffusion region and within each second diffusion region through substantially the same passageway area ratio.